Discontinuous Measurement Procedures: RBT Exam Guide (A3 Task List)

Discontinuous measurement procedures let you record whether a behavior occurred during parts of an observation instead of every single instance. For RBT candidates, mastering these methods is essential: partial interval, whole interval, and momentary time sampling produce useful estimates when continuous measurement isn't feasible, show up frequently on the RBT exam, and drive real-world decisions in classrooms and group settings. This guide gives you exam-focused definitions, step-by-step implementation, common pitfalls to avoid, quick study drills, and practice items tied directly to Task A‑3.

What Are Discontinuous Measurement Procedures?

Discontinuous measurement records samples of behavior during specific intervals or moments rather than every occurrence. This produces estimates — not exact counts — and works great when continuous measurement isn't practical (like when you're watching multiple clients or dealing with high-rate behaviors).

Here's how each method works:

• Partial interval recording: Mark an interval "yes" if the behavior happened at any time during that interval
• Whole interval recording: Mark "yes" only if the behavior occurred for the entire interval
• Momentary time sampling: Mark "yes" if the behavior is happening at the exact moment the interval ends

Why RBTs need to know this stuff:

• You'll use these methods constantly for group observation and high-rate behaviors
• Each method has built-in bias: partial interval tends to overestimate occurrence, whole interval tends to underestimate, and momentary time sampling bias depends on how often the behavior actually happens
• The BACB expects correct implementation including interval setup, timing, and scoring rules

What to Expect on the RBT Exam

The exam loves testing A‑3 with these question types:

Definition matching: You'll see descriptions like "occurred at any time during the interval" and need to pick "partial interval recording."

Scenario selection: Given a clinical situation, you choose which procedure fits best.

Implementation details: Questions about setting interval length, timing, and following scoring rules correctly.

Data interpretation: Identifying whether a method will over- or underestimate the real occurrence rate.

Method selection: Explaining why one approach works better given the behavior type, frequency, or staffing situation.

Watch for these exam clues:

• "At any time during the interval" → partial interval
• "For the entire interval" → whole interval
• "Exactly at the end of the interval" → momentary time sampling

Setting Up Each Method: The Nuts and Bolts

Getting your setup right determines whether your data actually helps or misleads your team.

Choosing Interval Length

Short intervals (5–10 seconds) give you better accuracy but mean more work. Long intervals (30–60 seconds) are easier to manage but introduce more bias. You'll need to find the sweet spot based on what you're measuring.

The Three Scoring Methods

Partial Interval Recording RBT candidates use this for brief, high-rate behaviors. Score "yes" if the behavior happened at any time during the interval. The catch? It tends to overestimate how often something really occurs because one brief instance counts for the whole interval.

Whole interval recording works for sustained behaviors like staying on-task. Score "yes" only if the behavior lasted the entire interval. This method underestimates because brief interruptions make you score "no" for the whole interval.

Momentary time sampling RBT supervisors love for efficiency. Check if the behavior is happening at the instant each interval ends. Great for watching multiple people, but you'll miss what happens between checks.

Tools You'll Need

• Timer with repeat function (your phone works fine)
• Simple recording sheet with interval numbers and yes/no columns
• Clear operational definition of your target behavior
• Plan for where you'll position yourself and what to watch first

Quick decision guide:

• Need exact counts → use continuous measurement instead
• Watching multiple clients → try momentary time sampling
• Brief, frequent behaviors → partial interval
• Must-be-sustained behaviors → whole interval

The Cooper et al. measurement chapter breaks down these decisions in more detail.

Step-by-Step Implementation Examples

Scenario 1: Partial Interval for Desk Tapping

You're watching a student who taps their desk constantly during work time.

Setup: 10-second intervals for a 5-minute session
How to do it: Start your timer. At the end of each 10-second interval, mark "yes" if any tapping happened during that interval, "no" if none occurred
Why this works: High-rate, brief behavior where counting every single tap isn't realistic

Scenario 2: Whole Interval for On-Task Behavior

You need to track whether a child stays focused on their worksheet.

Setup: 30-second intervals for a 10-minute session
How to do it: Mark "yes" only if the child worked continuously for the entire 30 seconds. Any break in attention = "no" for that interval
Why this works: Captures truly sustained engagement, though it'll underestimate brief lapses

Scenario 3: Momentary Time Sampling for Multiple Students

You're supervising 4 students and need engagement data on all of them.

Setup: Check each student at 15-second marks during a 20-minute session
How to do it: When your timer beeps, quickly scan each student and record whether they're engaged at that exact moment
Why this works: Only practical way to get data on multiple people simultaneously

Common Exam Trap: Wrong Method Choice

Watch out for scenarios that use partial interval to estimate total duration of long behaviors (like tantrums). Partial interval will inflate duration estimates — whole interval or continuous recording work better here.

Converting Your Data for Graphs

Say you collected 6 intervals (10 seconds each):

• Partial interval: Yes, Yes, No, Yes, Yes, No → 4/6 = 66.7% (likely overestimate)
• Whole interval: Yes, No, No, No, Yes, No → 2/6 = 33.3% (likely underestimate)
• Momentary sampling: Yes, No, No, Yes, No, No → 2/6 = 33.3%

Always convert to percentages: (yes intervals ÷ total intervals) × 100

Mistakes That Cost Points on the Exam

Mixing up scoring rules: Marking whole interval "yes" when behavior only happened part of the time — this is actually partial interval scoring.

Using partial interval for duration estimates: Without acknowledging it overestimates the actual time spent in the behavior.

Random interval lengths: Too long creates big bias, too short becomes impractical to manage.

Timer problems: Not resetting properly or missing the exact endpoint (crucial for momentary time sampling).

Vague definitions: If you can't clearly identify when a behavior starts and stops, your data won't be reliable.

Practice with timers, write crystal-clear operational definitions, and always check your reliability with others.

Study Strategies That Actually Work

Video practice: Score the same 10-minute clip using all three methods, then compare percentages to see bias patterns firsthand.

Scenario flash cards: Create 50 brief situations and practice picking the right method quickly.

Three-column cheat sheet: Method | Best for | Scoring rule. Review this right before the exam.

Live timing practice: Set different interval lengths and score real-time situations to build accuracy.

Reliability checks: Partner with someone and compare your data sheets — resolve disagreements by refining your definitions.

Research shows that interval sampling accuracy depends heavily on interval length and behavior characteristics, so practice with different combinations.

Practice Questions (RBT Style)

Question 1: Which procedure should you use when you need to know whether a child stayed seated and working for entire 15-second intervals?
Answer: Whole interval recording

Question 2: You're supervising 3 children and plan to check each one exactly at the end of every 20-second interval. What method are you using and what's one limitation?
Answer: Momentary time sampling; limitation — you'll miss behavior that happens between checks

Question 3: Using partial interval recording RBT style, you observed 8/12 intervals marked "Yes." What can you conclude?
Answer: Behavior occurred in 66.7% of intervals; partial interval likely overestimates actual duration, so treat this as an estimate

Last-Minute Review Essentials

• Partial = any part of interval → overestimates frequency/duration
• Whole = entire interval → underestimates occurrence
• Momentary time sampling RBT = snapshot at interval end → efficient but can miss stuff
• Pick your method based on behavior type (brief vs. sustained), rate, and how many people you're watching
• Always set clear intervals, sync your timer, and write precise definitions

Frequently Asked Questions

How do I pick the right interval length?

Go with the shortest interval you can actually manage. Shorter intervals reduce bias but require more attention. For high-rate behaviors, try 5–15 seconds. For sustained behaviors, 20–30 seconds might work fine. Test your choice with a quick pilot run.

When should I use momentary time sampling RBT methods over partial interval?

When you're watching multiple people or can't focus continuously on one person. Momentary sampling is super efficient but misses what happens between samples. Best when you need general estimates across several clients.

Can partial interval give me accurate duration data?

Not really. Partial interval inflates duration because any occurrence counts for the whole interval. If you need actual duration, use continuous duration recording or whole interval for behaviors that must be sustained.

How should I report this data to my supervisor?

Include the method (like "partial interval, 10-second intervals"), session length, total intervals, and percentage with behavior. Always mention the bias direction so your supervisor interprets trends correctly.

How can I improve my reliability with these methods?

Write super clear operational definitions, practice with the same video clips as your colleagues, and discuss any scoring disagreements to refine your criteria.

Ready for Success

Mastering discontinuous measurement procedures gives you major points on the RBT exam plus practical skills for real clinical work. Focus on nailing the scoring rules (partial = any time, whole = entire interval, momentary = snapshot), picking interval lengths that balance accuracy with feasibility, and practicing timed observations.

Your next steps: make that three-column cheat sheet, complete three 10-minute video scoring sessions (one per method), and run reliability checks with a peer before your exam. Solid practice now makes accurate, defensible data collection second nature in your clinical work.